Place potatoes in a small saucepan and cover with water. Bring to a boil. Reduce heat; cover and cook for 15-20 minutes or until tender. Drain. Sprinkle with vinegar. When potatoes are cool enough to handle, cube and place in a small bowl. Add the red pepper, peas, cucumber and onion; toss gently to combine. In a small bowl, combine the mayonnaise, sour cream, horseradish, salt and pepper. Pour over potato mixture; toss to coat. Cover and refrigerate until serving. Yield: 2 servings.